Manufacturers of cigarettes have long been desirous of accurately monitoring the firmness of a cigarette rod during making and thereafter for quality control purposes, and such monitoring heretofore has been accomplished in a number of ways. One procedure is that of employing the rod firmness testing apparatus described in U.S. Pat. No. 2,163,415 for detecting rod firmness and used for the purpose of regulating the amount of tobacco entering the machine. U.S. Pat. No. 3,572,101 describes apparatus for measuring the rod firmness of cigarettes after completion. Such methods as well as others known in the cigarette making art deal with measurements made during or after making of the cigarette and generally are carried out under ambient conditions of temperature and humidity. Such testing is not necessarily responsive to changes in cigarette blends and truly reliable as a basis for predicting the expected firmness of a given blend in a cigarette rod during smoking. As a cigarette is smoked and the heated products of combustion are drawn from the coal over the unburned tobacco rod into the smoker's mouth, the action of the heat on the rod of tobacco wets it with the moisture that is formed as a by-product of combustion as well as that moisture which is simply driven off from the tobacco by heat evaporation which occurs adjacent the burning coal. There is also a slight increase in temperature within the tobacco rod due to the passage of the hot smoke therethrough as it travels along the length of tobacco filler from the coal to the smoker's mouth.
A most important aspect of quality with which the manufacturer is concerned, is that feel of a cigarette based on a tobacco blend's characteristics affecting its ability to allow the cigarette to remain firm during smoking. Conventional tests of rod firmness, as they are now made during manufacture in the making equipment, or under laboratory conditions, do not reliably predict the degree of rod firmness to be expected for a given blend during smoking. The testing of rod firmness during smoking introduces effects based upon the above-described changes in the temperature and humidity of the rod which require different treatment in testing. A further set of complexities are introduced as a result of the progressive build-up of moisture to different levels at various points along the shortened rod length during smoking. The increased moisture content builds progressively as the hot smoke conducted through the rod from the combustion zone to the smoker's mouth cumulatively deposits moisture in the tobacco through the condensation of the hot vapors generated near the coal, and the effect of these moisture and temperature changes can be quite different for various tobacco blends.
It is an object of the present invention to provide a method and apparatus to determine in advance the effect that a firmness change due to moisture and heat have on the subjective fingertip impression that is made by a smoker, before lighting and then after several puffs have been taken for cigarettes made with particular blends of tobacco filler.